Author: pepijndevos

I wanted to make an EV3 tamagotchi with a friend, but after various experiments I found the Puppy that comes with the EV3 education set, which is way cuter than anything we designed so far. But the education version contains different parts than the retail version, so we could not build that one.

So I sat down to create a puppy with the parts from the retail edition of the EV3. The end results looks very similar, but the construction is quite different in places.

The only functional difference is that I did not add the touch sensor and added the infrared sensor instead. So you can’t pet this puppy, but it can detect when you’re near and track the beacon with its eyes.

Other than that it’s mostly the same as the educational version. It can tilt its head up and down, stand up and sit down, pee and display different emotions.

The code I wrote so far is only a dozen lines of Python, which I might upload later. The good news is that due to the Christmas holiday, I had time to make some nice building instructions, check them out!

I made another silly thing. I came across a musical instrument called a Theremin. The real deal uses a really cool concept where your body and 2 antennas act as a capacitor in an LC circuit. By changing the distance between your body and the antennas, the capacitance changes, which changes the resonance frequency and modifies the pitch and amplitude of the output signal.

This thing is much more silly. It uses the IR sensor to measure the distance to your hand and generates a tone based on that. It works nothing like the real thing.

The sound quality of the EV3 is terrible, because it’s just a small speaker attached to a PWM port with a low-pass filter.

The IR sensor is slow, inaccurate and discrete. So you can do none of the slides and vibrato you can do with a Theremin. At first I tried to smooth the input to get a more natural sound, but that made it even slower and impossible to tune. So in the end I mapped the discrete input steps to discrete notes, so that it at least sounds in tune. You still can’t play anything on it though.

I wrote the code for this in C on ev3dev. I use ev3c to talk to the sensors and libasound to generate the sound. This took a while to get working.

I wanted to invite someone over to watch a movie, but realised that my energy saving light bulb isn’t the most cozy environment ever. The light they give of always feels a bit cold.

To remedy this I went to the store to buy some candles (and forgot to buy matches). But just plain candles seemed so boring, so I wanted to do something special with them.

I remembered from years back this Tai Chi practice where you put glasses of water or candles on your hands and rotate them over and under your shoulder. It creates this beautiful spiral movement. So I thought it would be nice to make a robot that moves my candles around.

I have tried before to make a Rocker-Bogie robot, similar to NASA’s Mars rovers. But with the NXT I always had a shortage of structural parts, leading to incomplete and unstable constructions.

With the EV3 it works surprisingly well, and I was able to power all the wheels with two motors, and leave enough parts to make a robotic arm.

It looks lovely, and the principle works, but the actual capabilities are slightly disappointing as the torque is very limited. Climbing any large obstacles pushes the bogie off the ground and rattles some of the many gears.

After a long period of silence, I finally made some things with my EV3. Last time the tools where not really ready, but now everything works great.

I used ev3dev and python-ev3 to build this bulldozer. Watching sumo matches at LEGO World, I saw a few things that do and don’t work.

A lot of people seem to go for blades and hammers, but unless you actually want to destroy the robot, they are useless. Treads sound like a good idea, but wheels have more grip in practice. Make sure the wheels don’t fall off. Encased wheels are the best.

The goal is to push the other robot off the table, so the more powered rubber the better. Four wheel drive is better than rear wheel drive, but rear wheel drive is still much better than front wheel drive.

It’s all about pushing. The only useful thing besides pushing forward is pushing up or sideways. Pushing up is the easiest, because you have the floor to back you up. It also pushes the opponent’s wheels off the ground. This lead me to the following design.

Drive chain

Arm down

arm up

lifting a box

I used two pairs of driven rear wheels on a pivot, so even if I’m lifted, all four remain in contact with the ground. They are geared down, which means I’m slow, but powerful. All the weight of the motors and EV3 is directly above the wheel, for maximum grip.

On the front there is a lift arm, using a worm wheel and a very solid construction. I went through several iterations, improving the strength each time. On the first iteration, it was to weak, but its wedge shape still lifted my opponent a little.

The code is quite simple. Push forward. When you reach the edge, turn around. When something hits the bumper, raise the arm.

Today I took out the RCX and made a wheelbase for the NXT excavator arm I made earlier.

I am satisfied with the look and maneuverability, the only problem remains where to put the RCX. Maybe I can put both the NXT and the RCX on the arm, or make some room in the wheelbase.

It will also be interesting to control the whole maschine. The NXT and RCX can’t really talk to each other, but both can talk to the computer over Bluetooth and Infrared respectivly. So maybe I wil make a command centre on the computer to control both devices.